Communication devices such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless devices, wireless terminals, mobile stations and/or stations (STAs). Such terminals are enabled to communicate wirelessly in a wireless communications network such as a Wireless Local Area Network (WLAN) and/or a cellular communications network, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
These terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
In a wireless communications network such as a Wireless Local Area Network (WLAN), the communications device may further be referred to as a network node such as a WLAN node. The WLAN node may be an access node such as an Access Point (AP) or a station (STA).
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
In WLANs, a Clear Channel Assessment (CCA) Threshold (CCAT) is specified to define a range within which a WLAN node, e.g. an Access Point (AP) or a station (STA), will sense the transmission of other WLAN nodes to avoid transmission collision, e.g. interference.
Using a threshold based on received power regardless of which one of the WLAN nodes that is generating the interference is not optimal from a performance perspective, since WLAN nodes operating in the WLAN may be prevented from transmitting even though the transmission is likely to be successful and not disturb other ongoing transmissions. With adequate link adaptation it is possible to operate in reuse-1 mode, i.e. only defer from transmitting concurrently with transmissions from a WLAN node comprised in the same coverage area as the WLAN node intending to transmit.
WLAN, also known as Wi-Fi is standardized in the Institute of Electrical and Electronics Engineers (IEEE) “Standard for Information technology—Tele-communications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) 802.11 Specifications (IEEE 802.11 specifications). In this disclosure the terms Wi-Fi and WLAN will be used interchangeably. Wi-Fi is a technology that currently mainly operates on the 2.4 GHz or the 5 GHz frequency band. The IEEE 802.11 specifications regulate the WLAN nodes, e.g. the APs or STAs, PHY layer, MAC layer and other aspects to secure compatibility and inter-operability between APs and STAs. In this disclosure, the STA may also be referred to as a wireless device or a UE. Wi-Fi is generally operated in unlicensed bands, and as such, communication over Wi-Fi may be subject to interference sources from any number of both known and unknown WLAN nodes. Further, Wi-Fi is commonly used as wireless extensions to fixed broadband access, e.g., in domestic environments and hotspots, like airports, train stations and restaurants.
A Modulation and Coding Scheme (MCS) index is a value, e.g. an integer, describing the modulation type, code rate and number of streams used in a transmission. The MCS index starts at 0 corresponding to the lowest link bitrate. For a 20 MHz channel the MCS index goes up to 7, 15, 23, and 31 for 1, 2, 3, and 4 spatial streams, respectively. The higher the MCS index is, the more sensitive the transmission is to interference, but the transmission will carry a higher amount of data. The MCS index is selected by a process, e.g. an algorithm commonly referred to as link adaptation. This is a proprietary implemented algorithm that uses available knowledge of the channel quality, e.g. a Signal-to-Interference-Plus-Nose Ratio (SINR), situation. The knowledge is inferred through e.g. historical data on failure rates for transmissions with different MCS's.
The WLAN technologies rely on Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) in order to effectively and fairly share the wireless medium among the different WLAN nodes operating in the WLAN. The CSMA/CA may even be used to effectively and fairly share the wireless medium among different Radio Access Technologies (RATs). The CSMA/CA applied by the WLAN system demands that every device, e.g. WLAN node, that wishes to send data senses the common communication channel before carrying a transmission. This is in order to avoid duplicate transmissions that usually results in loss of data and in the need of retransmissions. In order for a device to deem the communication channel busy, it has to detect a transmission, and the received signal strength level of the detected transmission must surpass a pre-determined threshold. In this disclosure the pre-determined threshold is sometimes referred to as a Clear Channel Assessment (CCA) Threshold (CCAT). FIG. 1 schematically illustrates a wireless communications network according to prior art. The wireless communications network comprises an access point AP configured for communication with two stations, STA A and STA B, respectively, arranged in the wireless communications network. Further, the pre-determined threshold CCAT is schematically illustrated in FIG. 1. Thus, if one of the WLAN nodes comprised in the wireless communications network detects a transmission and if the the received signal strength level of the detected transmission surpasses the pre-determined threshold COAT, the WLAN node will deem the communication channel busy and defer from transmitting.
In current WLAN systems, one common COAT is defined for all WLAN nodes operating in the WLAN, and this common COAT is to be used when performing channel sensing for transmission to and from any WLAN node in the WLAN. Thereby, a WLAN node may be prevented from transmitting even though the transmission is likely to be successful and likely not to disturb other ongoing transmissions. This results in an inefficient usage of WLAN resources.